1. Field of the Invention
The present invention relates to an injection molding machine of an in-line screw type, and more particularly to a controller for controlling a metering process of an injection molding machine.
2. Description of Related Art
As for a conventional method of metering resin in an injection molding machine of an in-line screw type, it has been general to control a screw retracting force, namely a back pressure to be opposed to molten resin in a cylinder, in order to enhance kneading of resin by an injection screw. In this method, time needed for the metering is dispersed and utilized as a factor for determining whether the metering process is carried out successfully or not.
There is proposed a method of controlling a retracting speed of an injection screw to be held at a predetermined value in the metering so as to make the metering time constant, in Japanese Patent Publications Heisei 7-205228 and Showa 61-110524.
An object of the present invention is to provide a metering controller capable of making a metering time constant and kneading of resin uniform in a metering process of an injection molding machine.
According to one aspect of the present invention, a metering controller for an injection molding machine comprises: detecting means for detecting a rotational torque exerted on a screw; a memory to store the detected rotational torque in time series from a start of a metering process as reference torque; and a processor to correct a rotational speed of the screw based on the reference torque stored in the memory and a rotational torque of the screw detected in an actual metering process, thereby the screw rotational speed is controlled so that a transition pattern of the screw torque traces the transition pattern of the reference torque, thereby reducing dispersion of the metering time.
Instead of storing the detected torque of the screw in time series from a start of a metering process, the memory may store the detected torque with an axial position of the screw to be associated therewith in a metering process, and the processor corrects a rotational speed of the screw based on the reference torque stored in the memory and a rotational torque of the screw detected by the torque detecting means in an actual metering process.
In order to correct the rotational speed of the screw, the processor calculates a correction amount based on a deviation between the reference torque and the torque in the actual metering process, and corrects a predetermined rotational speed command for the screw based on the correction amount. The processor may restrict the correction amount not to exceed an upper limit or a lower limit set for the correction amount. Values of the rotational speed command may be respectively set for a plurality of stages of the metering process.
According to another aspect of the present invention, a metering controller for an injection molding machine comprises: a detector to detect a retracting speed of a screw; a memory to store the retracting speed detected by the detector in time series from a start of a metering process as reference retracting speed; and a processor to obtain a correction amount for a rotational speed of the screw based on the reference retracting speed stored in the memory and a retracting speed of the screw detected by the detector in an actual metering process, restrict the correction amount not to exceed an upper limit and a lower limit or the lower limit set for the correction amount, and correct the rotational speed of the screw in accordance with the correction amount. Command values of the rotational speed may be respectively set for a plurality of stages of the metering process.
Instead of storing the retracting speed detected by the detector in time series from a start of a metering process, the memory stores the detected retracting speed with an axial position of the screw to be associated therewith in a metering process, and the processor obtains a correction amount for a rotational speed of the screw based on the reference retracting speed stored in the memory and a retracting speed of the screw detected by the detector in an actual metering process, restricts the correction amount not to exceed an upper limit or a lower limit set for the correction amount, and corrects the rotational speed of the screw in accordance with the correction amount.
According to still another aspect of the present invention, a metering controller for an injection molding machine comprises: a position detector to detect an axial position of a screw; a memory to store the axial position detected by the position detector in time series from a start of a metering process as reference position; and a processor to correct a rotational speed of the screw based on the reference position of the screw stored in the memory and a position of the screw detected by the position detector in an actual metering process.
In order to correct the rotational speed of the screw, the processor calculates a correction amount based on a deviation between the reference position and the position of the screw in the actual metering process, and corrects a predetermined rotational speed command for the screw based on the correction amount. The processor may restrict the correction amount not to exceed an upper limit an a lower limit or the lower limit set for the correction amount. Values of the rotational speed command may be respectively set for a plurality of stages of the metering process.